1. Field of the Invention
The present invention relates in general to a method of quickly determining word line defect type in dynamic random access memory.
2. Description of the Related Art
Conventionally, defective word lines in memory, produced in the conventional DRAM process, may have small leakage currents such that the memory may not work correctly. Typically, there are several failure types of defective word lines that cause leakage current in the memory due to process defect. Types of defective word lines include a word line shorting to a bit line, a word line shorting to a word line and a word line shorting to the substrate due to pin holes in the gate oxide layer between the word line and the substrate.
Conventional methods to determine defective word line failure type perform an electric characteristic analysis to determine which word lines are defective. A physics analysis is then performed to determine defective word line failure types. The physics analysis repeatedly removes the surface of the memory by chemical solution and then checks the removed memory by an electron microscope. However, the physics analysis is time consuming and sometimes cannot determine the defective word line failure types.
An object of the present invention is to provide a method to quickly determine defective word line failure types. The method of the present invention quickly determines the defective word line failure type by performing an electric characteristic analysis.
In the embodiment of the present invention, a relational table of electric characteristic and defective word line failure types is formed. A defective word line is then activated, a first voltage is applied to the defective word line and the electric characteristic of the defective word line is measured simultaneously. Next, the defective word line failure type is determined according to the relational table and the measured electric characteristic.
In the second embodiment of the present invention, a relational table of electric characteristic and defective word line failure types is formed. A defective word line is activated, a second voltage is applied to a word line and the current on the word line is measured simultaneously. Next, it is determined whether the word line is defective according to the measured current, and the next step is carried out if the word line is a defective word line. Thereafter, a third voltage is applied on the defective word line, and the electric characteristic of the defective word line is measured. Next, the defective word line failure type is determined according to the measured electric characteristic and the relational table, and the defective word line is turned off. Next, another word line of the memory device is activated and the same processes are performed again.